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Questions and answer--listed in the order received

Please note!

Listed below are questions submitted by users of "The Exploration of the Earth's Magnetosphere" and the answers given to them. This is just a selection--of the many questions that arrive, only a few are listed. The ones included below are either of the sort that keeps coming up again and again--the danger of solar eruptions, the reversal of the Earth's magnetic field, etc.--or else the answers make a special point, going into extra details which might interest other users. Because this is a long list, it is divided into segments

However, when people talk about "radioactive radiation" or "radiation belts of the Earth" they mean a stream of fast particles, electrons,
ions or neutrons, which also spreads in space. Early researchers did not understand the difference and the name stuck.

"Irradiance" as I understand it means energy deposited per unit area. The Sun beams at Earth 1.36 kilowatt per square meter, the "solar constant." I think that is the irradiance due to sunlight, or would be if the
atmosphere did not scatter some of it back, and if the receiving area
is perpendicular to sunlight.

"Solar Terrestrial Radiation" I have not heard before. Solar Terrestrial Physics is the term usually applied to the particles sent out by the Sun, the magnetic fields they are embedded in and the phenomena these produce near Earth (see my web site with home page
http://www.phy6.org/Education/Intro.html)

In other words, the Sun sends us MORE than just electromagnetic radiation. I would think the term excludes the solar wind but includes higher energy stuff--see for instance "Birth of a Radiation Belt" at the end of the above web site. "Solar Extraterrestrial Radiation" I cannot even guess.

In 1985 German scientists of the AMPTE mission exploded a charge of
barium in the solar wind. The ions of barium vapor were quickly ionized
by sunlight, creating an "artificial comet" of barium ions. The "comet"
cloud was then quickly captured by magnetic field lines embedded in
the solar wind, which made it share the flow velocity of the solar wind.

37-b The Size of the Magnetosphere

Dear Professor,

I am an Italian student of Physics and I met your very
beautiful site
http://www.phy6.org/earthmag/, and I have a
question for you.
I would like to know exactly the size of the
magnetosphere, say from the Earth's surface up to the
magnetopause, compressed in the day part and elongated
into the magnetotail in the night part.

I thank you very much for your kind attention!

Reply

The average distance to the dayside "nose of the magnetosphere"
("subsolar point" in phys-speak) is about 10.5 Earth radii or some 67,000
kilometers. On the flanks, 90 degrees from there, the distance is about
15 Earth radii, and ithe flanks continue to approach a cylinder, about 25
Earth radii in radius.

At midnight there is no clear boundary. What happens, apparently, is
that past 50-80 Earth radii the solar wind infiltrates the magnetotail,
so the material is mostly solar wind, but the magnetic field is still
that of Earth. It goes like this for at least 220 Earth radii.

But mind you, these are averages. When the pressure of the solar wind
rises, the boundary moves inwards. It also does so if the interplanetary
magnetic field slants southward, which "erodes" the magnetic field by a
reconnection process. A few times each year, therefore, the boundary
passes satellites in synchronous orbit, at 6.6 Earth radii. On the other
hand, in 1999 an instance occurred when the solar wind was very
rarefied, and the noon-side boundary went out past 20 Earth radii.